1. Field of the Invention
Embodiments of the invention relate to a method of fabricating a semiconductor device. More particularly, embodiments of the invention relate to a method of forming a fine pattern on a substrate using a fine pitch hard mask.
2. Description of Related Art
Large scale integration of semiconductor devices has generally required the use of micronized patterns. Individual devices must be micronized in order to integrate a great multiplicity of devices within a limited area. As a result, it is commonly necessary to scale down the pitch of various patterns used to form the devices. As the design rules for semiconductor devices have rapidly shifted towards micronization, it has become increasingly difficult to form sufficiently fine pitch patterns due to the resolution limitations of conventional photolithography processes used to form the patterns. However, such very fine line and space patterns (hereinafter referred to as “L/S patterns”) are necessary to the implementation of contemporary and emerging semiconductor devices on various substrate materials.
Among the various methods proposed to improve the resolution of conventional photolithography processes, one method suggests patterning an etch target layer using a hard mask spacer pattern. In particular, the spacer pattern may be formed using a specific method, such as the one disclosed, for example, in U.S. Pat. No. 6,603,688, which is adapted to the formation of a spacer having small feature sizes.
However, if this type of spacer pattern is used as the hard mask, the thickness of each one of a paired set of spacers formed on sidewalls of a particular pattern will generally be non-uniform. Hence, it is typical to form a spacer thicker than its intended pattern thickness in order to obtain uniformity of the thickness for paired spacers. This thickened spacer also makes it difficult to remove the spacer pattern after the spacer pattern is used as the hard mask. Since the aforementioned hard mask is formed by encompassing both sidewalls of the aforementioned particular pattern by the pair of spacers, when forming line patterns using the spacers, an additional trimming process is generally required to separate the spacers into an individual line pattern.
When patterns must be formed in one region having a relatively high pattern density—for instance, a cell array region in a semiconductor substrate, and in another region having a relatively low pattern density—for instance, a peripheral or core region it may be necessary in view of the foregoing limitations to form these respective patterns separately. That is, when it is necessary to form desired patterns having very different pitches, as between different regions of a substrate, it is often necessary to form these different pattern pitches separately. This requirement further complicates the process of fabricating semiconductor devices on substrates and tends to drive up the associated costs and risks of patterning errors.